Manufacturing electric devices having sealed envelopes

ABSTRACT

A method of dosing an envelope of an electric device such as a lamp with a gaseous or volatile substance, e.g. mercury in a discharge lamp, entails containing the substance inside a sealed capsule and putting the capsule inside the envelope, the dosing substance being released into the envelope at some convenient point during the manufacturing cycle by perforating the capsule using the intense heat developed when a beam of radiation from a laser is focussed to spot upon the capsule.

United States Patent 11 1 Clarke 1 Oct. 21, 1975 1 MANUFACTURING ELECTRIC DEVICES HAVING SEALED ENVELOPES [75] lnventor: Maurice George Clarke, London,

England [73] Assignee: Thorn Electrical Industries Limited, London, England [22] Filed: Aug. 13, 1973 [21] Appl. No.: 387,594

[30] Foreign Application Priority Data Aug. 11, 1972 United Kingdom............... 37643/72 [52} US. Cl. 316/4; 219/121 LM; 313/177; 313/174; 316/3; 316/24; 316/25 [51] Int. Cl. 1101.1 9/395 [58] Field of Search 316/25, 16, 3, 4, 17, 18, 316/19, 20, 24; 313/174, 177; 417/48;

219/121 L, 121 LM [56] References Cited UNITED STATES PATENTS 3,291,549 12/1966 Campbell et a1 316/21 3,300,037 l/l967 De Santis 417/48 3,510,189 5/1970 Larson et al...... 316/3 3,580,654 5/1971 Kupsky 316/20 3,684,345 8/1972 Schiekel et a1. 316/4 3,794,402 2/1974 Ridders et al 316/25 X OTHER PUBLICATIONS H. F. Winters, Gettering By Laser Induced Evaporation, IBM Technical Disclosure Bulletin, Vol. 9 No. 10 Mar. 1967, p. 1365.

T. A. Osial, Industrial Laser Applications, Instruments & Control Systems, Oct. 1967, pp. 101-104. Stickley, Applications of Lasers, Special Reports No. 15, US. Air Force, Cambridge Research Laboratories, Nov. 1964, pp. 28-31.

Primary Examiner-Granville Y. Custer, .lr. Assistant Examiner-James W. Davie Attorney, Agent, or FirmRobert F. O'Connell [5 7] ABSTRACT A method of dosing an envelope of an electric device such as a lamp with a gaseous or volatile substance, e.g. mercury in a discharge lamp, entails containing the substance inside a sealed capsule and putting the capsule inside the envelope, the dosing substance being released into the envelope at some convenient point during the manufacturing cycle by perforating the capsule using the intense heat developed when a beam of radiation from a laser is focussed to spot upon the capsule.

7 Claims, 2 Drawing Figures U.S. Patent 0a. 21, 1975 MANUFACTURING ELECTRIC DEVICES HAVING SEALED ENVELOPES The present invention relates to improvements in the manufacture of electric devices having sealed envelopes such as lamps, valves and the like.

In particular, the present invention resides in the manner of introducing volatile and/or gaseous constituents into envelopes during manufacture of lamps, valves and the like the introduction of such constituents being known, inter alia, as dosing.

According to the present invention, there is provided a method of manufacturing electric devices having envelopes which contain dosings of at least one volatile and/or gaseous constituent, the method including the steps of placing a sealed capsule containing dosing substance inside an envelope, sealing the envelope and after sealing, perforating the capsule by directing a beam of radiation from a laser through the envelope and focussing the beam onto the surface of the capsule, thereby enabling the dosing substance to be released into the interior of the envelope.

The method is particularly applicable to discharge lamps such as fluorescent lamps, although is not restricted thereto. Thus, the method can be employed when making such lamps as tungsten-halogen filament lamps. In that case, the dosing substance within the sealed capsule is a volatile halide or halogen. When manufacturing a fluorescent lamp, the sealed capsule will normally contain mercury alone, and when manufacturing other forms of discharge lamp, the capsule will contain e.g. mercury or sodium along with additional substances which may be included to secure given discharge characteristics. It is important, when making a fluorescent lamp, to leave an area of its envelope clear of phosphor so that the said area is transparent to the laser beam.

In carrying out the method, the sealed capsules may contain substances which will form the gaseous fillings and/or ignition gases in the finished devices.

The sealed capsules can be made from any material which can be breached by means of the intense heating developed by the focused laser beam. A suitable laser would provide a radiation pulse of the order of i .loules energy at 1.06 microns energy, the pulse lasting about I millisecond. When this energy is focused onto a spot approximately h mm diameter, it will breach capsules of metal and even glass or silica, but will not affect the envelope providing the beam is defocused to cover an area of the envelope equal to square millimetres or more.

When manufacturing devices such as lamps, it is preferred, although not essential to include in the capsule or to make the capsule itself from a metal that exhibits gettering." In this connection, the capsule can be made from aluminium which is capable of combining with oxygen thereby acting as a getter. The getter is provided by the aluminium which evaporates from the capsule upon application of the focused laser beam, the evaporated aluminium depositing on the adjacent part of the lamp envelope. The use of aluminium is particularly advantageous when dosing lamps with mercury since mercury and aluminium form an amalgam that is an especially effective getter.

Gettering can be used in the production of high vacua and may be regarded as chemical pumping (see, for example, Vacuum Technology. Aa introduction, by L. G. Carpenter, published by Adam Hilger, London (1970), and is also used to remove selected gases which are unwanted in devices such as electric lamps having chosen fillings.

The action and nature of getter materials are described in Chapter 18, entitled "Getter Materials" of the Handbook of Materials and Techniques for Vacuum Devices, by Walter H. Kohl, published by the Reinhold Publishing Company of New York, Amsterdam and London, in I967 (Library of Congress Catalogue Card No. 67-18288).

The invention will now be described in more detail by way of example with reference to the accompanying drawings, wherein FIG. 1 is a sectional view of an end portion of a first discharge lamp according to the invention, and

FIG. 2 is a sectional view of an end portion of a second discharge lamp according to the invention.

The lamp 10 shown in part in the drawing is a fluorescent lamp which has a glass envelope tube 11, the major part of whose inner surface has a phosphor coating 12. The coating is applied in a known manner and the extreme end region 13 of the envelope 11 is left clear of the coating 12. An inwardly-projecting neck 14 is fused to the end of the envelope 12, the neck 14 having two electrode lead-wires l6 sealed therein. The electrode wires 16 carry an electrode heater filament 17 at their inner ends. Finally, the neck 14 incorporates and seals an exhaust and gas-filling tube 18 which is used during manufacturing the lamp.

In making the lamp 10, a sub-assembly is first constructed by sealing the filament lead-wires [6 into the neck 14, together with the tube 18 which at this stage is open at both its ends. A sealed capsule 20 containing a globule of mercury 21 is attached to one of the lead wires 18 of the sub-assembly by means of a spur-wire 22 welded thereto. The spur-wire 22 can be tightly wrapped around the capsule 20. The formation and filling of the capsule will be described in greater detail later.

The sub-assembly is then inserted and fused into one end of the phosphor-coated envelope tube I1. A similar sub-assembly is fused to the other end of the envelope 11 forming a sealed closure. This sub-assembly differs from the illustrated sub-assembly in that there is no need for it to include a sealed capsule 20 and tube 18.

The tube 18 is then attached to an exhausting and gas-filling maching which evacuates and then fills the envelope 11 with a gas-filling or argon to an appropriate pressure. The tube 18 is sealed.

After sealing, the next step is to release the mercury 21 within the capsule 20. To do this, a beam of radiation 25 from a laser is directed through the transparent end region 13 of the envelope 11 and is brought to a focus on the capsule 20. The resulting intense heating thereof produces perforation of the capsule 20. Care must be taken not to focus the radiation 25 onto the end region 13 instead of onto the capsule, otherwise the region 13 will be strongly heated and will perforate.

The capsule must be designed to withstand the processing conditions necessary for fabricating the device. In particular, it must withstand the temperatures experienced during the scaling in and during any subsequent baking for outgassing during exhaustion.

A relatively soft material such as aluminium may be preferred for reasons to be described, but a relatively large capsule may be necessary so that the processing temperatures does not burst the capsule due to high internal mercury vapour pressure. Alternatively, an iron or steel capsule may be employed as it will withstand higher internal pressure.

The capsule 20 can be manufactured as follows. A long, narrow, thin-walled aluminium tube is closed at one end by nipping between two hard steel rollers which, for instance, may be 4-6 millimetres in diameter. Nipping cold welds the aluminium, and effectively seals the closed end. The tube is then supported vertically, closed-end down, and the required quantity of mercury for one lamp is dropped into the tube. The size of the tube should be 2-3 times the diameter of the mercury globule to ensure that the mercury will drop freely to the bottom of the tube. Insertion of the mercury can be accomplished, if preferred, by means of a cannula. The tube is then evacuated and, if desired, filled with gas e.g. argon or a discharge ignitionpromoting gas. Thereafter, the tube is nipped again between the rollers to cold weld and seal the tube, thereby forming the sealed capsule 20. The final nipping step can be arranged to sever the sealed capsule from the rest of the tube. The remaining length of tube will already be closed at its lower end ready for making a subsequent capsule. The process is repeatable at considerable speed. Introduction of mercury can, if needed, be accelerated by alternate evacuation and pressurisation of the tube.

The use of aluminium as the capsule material has various advantages, amongst which are its cheapness, lightness and ductility, the ease with which it can be cold welded and its relatively low melting point. Aluminium also possess the valuable property that it can act as an efficient getter. This is because aluminium is able to combine with residual oxygen in the sealed envelope 11 to form a very stable oxide. When the beam of laser radiation is focussed onto the capsule 20, the evaporated aluminium is found to migrate preponderantly back along the laser beam i.e. towards the source of the beam. A thin gettering film of aluminium then deposits on the inner surface of the envelope 11, mainly in the end region 13. The area of the film can be controlled by varying the size and intensity of the focussed spot of radiation. Further gettering action can occur during use since aluminium tends to "sputter" in the presence of the arc discharge.

The gettering action can be further enhanced by including a piece of a gettering metal in the capsule 20. For a fluorescent lamp or mercury discharge lamp, it is preferred that the gettering metal should be one which will form on amalgam with mercury. Excess mercury would be provided initially in the capsule. The sputtered metal and the metal remaining in the capsule after perforation will then, in a known manner, control the mercury vapour pressure within the lamp and hence its operating temperature.

Aluminium itself acts as a highly efficient getter in the presence of mercury and hence the combination of these two metals is advantageous in applying the invention to the manufacture of fluorescent lamps, mercury discharge lamps and also sodium discharge lamps. in sodium lamps, mercury is often added as a buffer to produce desired electrical characteristics. When the capsule aluminium is wetted by mercury, some dissolution of aluminium occurs. The dissolved aluminium can then be oxidized at the mercury surface. The resulting oxide layer is not a tenacious, self-sealing protective film unlike the film which forms on solid aluminium. Thus, the gettering action can continue until all the available oxygen is converted to stable oxide. The gettering action can be initiated and promoted by heating the sealed capsule to around 250C. In this way, any oxygen inadvertently or unavoidably remaining in th. sealed capsules can be rendered harmless prior to their installation in lamp envelopes.

The aluminium/mercury amalgam is a particularly efficient getter. [n tests, it has been found possible to remove virtually all the free oxygen from a sealed capsule initially containing air at NTP, by annealing the capsule for one hour at 250C. Normally, of course, a sealed capsule would be evacuated or filled with an insert gas rather than air.

The sealed capsule 20 has been described as being mounted on one of the lead-wires 16, where it remains a permanet feature of the finished lamp. The capsule could, instead, be located within a tubulation which opens into the interior of the envelope. The tubulation can be a side arm or an appropriately-sized exhaust tube such as 18 which at this stage forms an integral part of the envelope as shown in FIG. 2. After releasing its contents into the envelope, the tubulation can be tipped off and thereby detached from the envelope, complete with the spent capsule.

Laser activated gettering techniques are disclosed in our co-pending application, filed on the same day as the application, and entitled: Improvements in or relating to gettering."

I claim:

1. [n a method of manufacturing an electric device having a sealed envelope containing a dosing of at least one constituent in the vapour phase, the steps of:

sealing dosing substance inside a capsule formed of a material selected from the group consisting of aluminium, iron and steel,

placing the sealed capsule inside an envelope and thereafter sealing said envelope, and

directing a focussed beam of radiation from a laser outside said envelope onto the surface of said capsule, whereby the heat generated by said focussed beam causes said capsule to perforate and release said dosing substance.

2. A method according to claim 1, wherein said capsule comprises an aluminium tube, said tube being nipped to close one end, evacuated and charged with dosing substance, said tube thereafter being nipped again to form a sealed chamber containing said dosing substance.

3. A method according to claim 1, wherein said capsule is attached permanently to a mounting inside said envelope.

4. A method according to claim 1, for use in the manufacture of a regenerative tungsten-halogen lamp, wherein said dosing substance inside said capsule includes a volatile halide or halogen.

5. A method according to claim 1, for use in the manufacture of a vapour discharge lamp, wherein said dosing substance inside said capsule includes mercury.

6. A method according to claim 5, for use in the manufacture of a fluorescent lamp, wherein said capsule is mounted adjacent one end of a phosphor-coated envelope, the phosphor coating being omitted from an end region of said envelope adjacent said capsule to allow the laser radiation to pass through said envelope to reach said capsule.

to form a continuous enclosed space extending within said tubulation and said envelope; directing a focussed beam of radiation from a laser outside said envelope and said tubulation on the surface of said capsule. whereby the heat generated by said focussed beam causes said capsule to perforate and release said dosing substance; and tipping off and detaching from said envelope the said tubulation complete with the spent capsule.

i t l 

1. In a method of manufacturing an electric device having a sealed envelope containing a dosing of at least one constituent in the vapour phase, the steps of: sealing dosing substance inside a capsule formed of a material selected from the group consisting of aluminium, iron and steel, placing the sealed capsule inside an envelope and thereafter sealing said envelope, and directing a focussed beam of radiation from a laser outside said envelope onto the surface of said capsule, whereby the heat generated by said focussed beam causes said capsule to perforate and release said dosing substance.
 2. A method according to claim 1, wherein said capsule comprises an aluminium tube, said tube being nipped to close one end, evacuated and charged with dosing substance, said tube thereafter being nipped again to form a sealed chamber containing said dosing substance.
 3. A method according to claim 1, wherein said capsule is attached permanently to a mounting inside said envelope.
 4. A method according to claim 1, for use in the manufacture of a regenerative tungsten-halogen lamp, wherein said dosing substance inside said capsule includes a volatile halide or halogen.
 5. A method according to claim 1, for use in the manufacture of a vapour discharge lamp, wherein said dosing substance inside said capsule includes mercury.
 6. A method according to claim 5, for use in the manufacture of a fluorescent lamp, wherein said capsule is mounted adjacent one end of a phosphor-coated envelope, the phosphor coating being omitted from an end region of said envelope adjacent said capsule to allow the laser radiation to pass through said envelope to reach said capsule.
 7. A method of manufacturing an electric device having a sealed envelope containing a dosing of at least one constituent in the vapour phase, comprising the steps of providing a tubulation attached to said envelope and opening to the interior thereof; sealing dosing substance inside a capsule formed of a material selected from the group consisting of aluminum, iron and steel; placing the sealed capsule inside said tubulation and thereafter sealing said tubulation and said envelope to form a continuous enclosed space extending within said tubulation and said envelope; directing a focussed beam of radiation frOm a laser outside said envelope and said tubulation on the surface of said capsule, whereby the heat generated by said focussed beam causes said capsule to perforate and release said dosing substance; and tipping off and detaching from said envelope the said tubulation complete with the spent capsule. 